The all-but-declared Republican presidential contender, who has kept his head low as he collected cash, brought together his network of wealthy donors on Monday to dial for dollars in a city with no shortage of them.

Romney's phone bank fundraiser at the Las Vegas Convention Center, much like one during his first attempt at the GOP nomination, was the centerpiece of a series of fundraising events that included a conference call with volunteers who were asked to solicit their friends and neighbors for donations.

"This is a big kickoff for us, for our fundraising effort. It's kind of a celebration," Romney told the more than 400 supporters tuned in to watch him host a brief town hall-style broadcast on Facebook. "It's important to me that we get that started, the ball rolling today."

In truth, the former Massachusetts governor has spent the better part of the year raising money for a campaign he has yet to officially launch.

He's held few political events in recent months, focusing almost entirely on private meetings with donors nationwide. He wants to emerge from the fundraising quarter that ends June 30 having far outraised his rivals, and displaying financial fortitude in hopes that Republicans will choose him to challenge President Barack Obama. The Democrat shattered fundraising records in 2008 and could raise as much as $1 billion for his re-election campaign.

A wealthy former businessman who is a Mormon, Romney is trying to tap into Wall Street and Mormon donors as well as line up support from influential contributors who fueled the campaigns of George W. Bush and John McCain. It's unclear whether he will invest any of his own fortune into his second campaign.

During his 2008 run for the GOP nomination, Romney used more than $40 million of his own money to pay for campaigns in Iowa and New Hampshire. Victories there never materialized, and Romney ended up losing the nomination to McCain.

Romney launched that bid with a phone bank fundraiser in Boston in which 400 supporters and Romney raised more than $6.5 million. But while that event was open to reporters, Romney's camp was much more guarded this time in Las Vegas. Aides refused to allow reporters into the phone bank room, and they wouldn't say how much they hoped to raise or how much his second White House bid would cost.

Volunteers who paid their own way to Las Vegas began trickling into the convention hall before sunrise to dial contacts on the East Coast who were already starting their work day.

Romney spent part of his day crisscrossing the phone bank room, which was flanked by two oversize American flags. Hundreds of volunteers called their contacts for credit cards numbers and contribution pledges. A sign read: "Believe in America."